1. Field of the Invention
The present invention generally relates to a system and a method for simulating an animation cloth and a recording medium thereof, in particular, to a system and a method for multilevel simulation of an animation cloth and a computer-readable recording medium thereof.
2. Description of Related Art
In a computer animation or a computer game, in order to render fine cloth dynamics or to process complicated impact detection between a piece of cloth and other objects, the piece of cloth is usually rendered with a grid model composed of mass-springs (as shown in FIG. 1) and simulated in real time through a physical simulation method.
The physical simulation method is to simulate real life physical phenomena in a computer program with mathematical calculations. Generally speaking, the physical simulation method is to calculate the total force (for example, including the gravity, an inertial force, and an external force etc) received by an object at a particular time point. For example, the mass point 1 in FIG. 1 receives bending forces from the mass point 2 and mass point 3, stretch forces from the mass point 4 and mass point 5, and a shear force from the mass point 6. After that, the acceleration produced by the total force is integrated into a velocity by using an integrator, and then the velocity of the object is integrated into a displacement, so that the movements of the object after it receives these forces can be obtained. The same movement of the object as in the real world can be simulated as long as the integrator is designed to conform to physical law.
However, a large quantity of calculations is to be done for simulating cloth animation in real time by using a simulation module established on the physical simulation method, and the calculation speed is very slow and instable. Thus, conventionally, in a multi-player or on-line game, cloth simulation is implemented based on a level-of-detail (LOD) model according to the availability of computer resources and the distance of the character or scene, so as to reduce the physical calculations. In other words, according to the existing LOD model, when a character is farther in the scene, the character is rendered with lower resolution so as to reduce the complexity of the model structure and the physical calculations by sacrificing fineness of the object.
FIG. 2(a) illustrates a piece of cloth rendered with different resolutions, wherein the resolutions of the cloth decrease from left to right. According to foregoing LOD model, the farther the scene is focused, the lower resolution in which the frame is rendered, and the closer the scene is focused, the higher resolution in which the frame is rendered. By this means, the calculation of the physical simulation method is reduced. FIG. 2(b) illustrates a piece of cloth in four different grid resolutions rendered in the same physical state, and FIG. 2(c) illustrates the results at a different time point. As shown in FIGS. 2(b) and 2(c), the animation cloth rendered with high and low resolutions looks very different. Thus, the conventional technique which reduces the calculation by rendering the object with low resolution will reduce the fineness of the object in a frame. Accordingly, a method for simulating an animation cloth which can reduce the calculation of the physical simulation method without sacrificing the resolution of the animation cloth is needed to be provided.